This invention relates in general to an apparatus for performing a hydroforming operation on a closed channel workpiece. In particular, this invention relates to an improved structure for such a hydroforming apparatus that is relative simple and inexpensive in structure and operation and is well suited for performing a hydroforming operation on relatively long workpieces, such as side rails for a vehicle frame assembly.
Hydroforming is a well known metal working process that uses pressurized fluid to deform a closed channel workpiece, such as a tubular member, outwardly into conformance with a die cavity having a desired shape. A typical hydroforming apparatus includes a frame having two or more die sections that are supported thereon for relative movement between opened and closed positions. The die sections have cooperating recesses formed therein that together define a die cavity having a shape corresponding to a desired final shape for the workpiece. When moved to the opened position, the die sections are spaced apart from one another to allow a workpiece to be inserted within or removed from the die cavity. When moved to the closed position, the die sections are disposed adjacent to one another so as to enclose the workpiece within the die cavity. Although the die cavity is usually somewhat larger than the workpiece to be hydroformed, movement of the two die sections from the opened position to the closed position may, in some instances, cause some mechanical deformation of the hollow member. In any event, the workpiece is then filled with a fluid, typically a relatively incompressible liquid such as water. The pressure of the fluid within the workpiece is increased to such a magnitude that the workpiece is expanded outwardly into conformance with the die cavity. As a result, the workpiece is deformed or expanded into the desired final shape. Hydroforming is an advantageous process for forming vehicle frame components and other structures because it can quickly deform a workpiece into a desired complex shape.
In a typical hydroforming apparatus, the die sections are arranged such that an upper die section is supported on a ram of the apparatus, while a lower die section is supported on a bed of the apparatus. A mechanical or hydraulic actuator is provided for raising the ram and the upper die section upwardly to the opened position relative to the lower die section, allowing the previously deformed workpiece to be removed from and the new workpiece to be inserted within the die cavity. The actuator also lowers the ram and the upper die section downwardly to the closed position relative to the lower die section, allowing the hydroforming process to be performed. To maintain the die sections together during the hydroforming process, a mechanical clamping device is usually provided. The mechanical clamping device mechanically engages the die sections (or, alternatively, the ram and the base upon which the die sections are supported) to prevent them from moving apart from one another during the hydroforming process. Such movement would obviously be undesirable because the shape of the die cavity would become distorted, resulting in unacceptable variations in the final shape of the workpiece.
As mentioned above, the hydroforming process involves the application of a highly pressurized fluid within the workpiece to cause deformation thereof. The magnitude of the pressure of the fluid within the workpiece will vary according to many factors, one of which being the physical size of the workpiece to be deformed. When a relatively small or thin-walled workpiece is being deformed, the magnitude of the pressure of the fluid supplied within the workpiece during the hydroforming operation is relatively small. Accordingly, the amount of the outwardly-directed force exerted by the workpiece on the die sections during the hydroforming operation is also relatively small. In these instances, only a relatively small amount of inwardly-directed force is required to be exerted by the hydroforming apparatus to counteract the outwardly-directed force so as to maintain the die sections in the closed position during the hydroforming operation. Consequently, the physical size and strength of the hydroforming apparatus when used for deforming relatively small or thin-walled workpieces is no greater than a typical mechanical press for performing a similar operation.
However, when a relatively large or thick-walled workpiece is being deformed (such as is found in many vehicle frame components, including side rails, cross members, and the like), the magnitude of the pressure of the fluid supplied within the workpiece during the hydroforming operation is relatively large. Accordingly, the amount of the outwardly-directed force exerted by the workpiece on the die sections during the hydroforming operation is also relatively large. To counteract this, a relatively large amount of inwardly-directed force is required to be exerted by the hydroforming apparatus to maintain the die sections in the closed position during the hydroforming operation. Consequently, the physical size and strength of the hydroforming apparatus is as large or larger than a typical mechanical press for performing a similar operation. This is particularly troublesome when the workpiece is relatively long, such as found in side rails for vehicle frames. The cost and complexity of manufacturing a conventional hydroforming apparatus that is capable of deforming such a workpiece is very high. Thus, it would be desirable to provide an improved structure for a hydroforming apparatus that is capable of deforming relatively large and thick-walled workpieces, yet which is relatively small, simple, and inexpensive in construction and operation.